The following URL can be used to check a site for malware :-
http://www.google.com/safebrowsing/diagnostic?site=example.com
This diagnostic URL works to check any site by replacing the domain at the end with the site you wish to check.
http://www.google.com/safebrowsing/diagnostic?site=xxxxxxxx.xxx
Found out that your website is infected?
This page has some info on what to do if your site has been infected :-
http://support.google.com/webmasters/bin/answer.py?hl=en&answer=163633
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